The present invention relates to the field of cooking fume extractor hoods for domestic use. The invention relates, in particular, to a controlled flow grease filter for trapping and separating liquid and/or solid particles suspended in the air from fumes sucked in by the extractor hoods.
In order to trap the microscopic particles suspended in the cooking fumes carried by domestic extractor hoods, the hoods are normally fitted with filters. These hood filters may be broadly divided into two main types, according to their constructional design.
In a first type of filter, multi-layered materials such as paper, cellulose or fine-mesh netting are used to trap and hold the liquid droplets or solid particles transported by the flow of fumes flowing through the filter while the part of the fumes constituted by air is allowed to flow through the filter.
The second type of filter comprises labyrinth filters which work on the principle of sudden changes of direction of fume flow. The fumes flowing through the filter are forced to follow a complex path having specially designed twists and turns. The part of the fumes constituted by air easily follows the path and flows out to the other side of the filter, whilst the suspended liquid droplets and solid particles are unable to change their direction suddenly on account of their high inertia and remain trapped inside the filter.
In a prior Italian patent application N. RN2002U000020, the Applicant disclosed a technical solution relating to labyrinth filters for domestic extractor hoods.
That solution, although tested successfully, has one drawback—common to all types of labyrinth filters—and that is, that, in strictly fluid dynamic terms, labyrinth filters can be advantageously used in extractor hoods only if the flow sections are relatively wide. Narrower flow sections reduce the working flow rate of the processed flow and increase flow speed. The former reduces the amount of air processed per unit of time, the latter exponentially increases load losses and significantly increases the noise made by the hood in operation. On the other hand, wider flow sections to improve the fluid dynamic properties of the filter would lead to a lower particle retention efficiency.
The aim of this invention is to overcome the above mentioned typical shortcomings of labyrinth filters by reaching an effective compromise that permits the achievement of a high suspended particle retention efficiency accompanied by low energy load loss and low noise.